Papillomaviruses induce a variety of lesions both in humans and in animals. Some papillomas, albeit benign, are themselves a clinical problem, such as laryngeal papillomas of children (Steinberg and Abramson, 1985) or penile papillomas of bulls (Jarrett, 1985a), and others are known to be a risk factor in the pathogenesis of cancer, as in the case of flat lesions of the cervix or penile condylomata in humans (zur Hausen, 1978). Therefore both in human and veterinary medicine the introduction of an anti viral vaccine, would be of major importance.
International Patent Application No. PCT/GB 92/01092 relates to the use of papillomavirus L2 protein as a therapeutically effective component in the treatment of papillomavirus tumours or lesions. In the examples, it is stated that the L2 open reading frame (ORF) of BPV-4 was cloned as the whole L2 ORF (encoding amino acids--8 to 525) and as three fragments encoding amino acids 11 to 201, 203 to 329 and 330 to 525. In subsequent vaccination experiments mixtures of the above amino acid sequence fragments were used in vaccination compositions. However, the identification of the active fraction capable of conferring immunity to papillomavirus and by extension to papillomavirus related diseases was not attempted. Other workers have reported that the L2 protein of cottontail rabbit papillomavirus (CRPV) is a prophylactic vaccine in rabbits [Christensen et al., Virology, (181, pp 572-579 (1991); Lin et al., Virology, 187, pp 612-619 (1992)] and the L2 protein of BPV-4 in cows (Campo et al, J.gen.virol. 74, pp 945-953 (1993). Christensen et al used the terminal carboxyl half of the L2 protein (amino acids 259-492) of CRPV and Lin et al used an L2 protein of CRPV from amino acid number 67-489. Neither group suggested employing a polypeptide comprising a portion corresponding to the active N-terminus of BPV-4 L2 (amino acids 11-200). Further workers, expressed the complete BPV-1 L1 and L2 proteins in E. Coli. The L1 protein was used to vaccinate calves and this resulted in a degree of protection from challenge with BPV-1 (Pilacinski et al., Papillomaviruses: Molecular and Clinical Aspects, UCLA Symposium 2, (1985), pp 257-271). It was also reported that rabbit antisera raised against L1 or L2 were capable of neutralising BPV-1 in transformation assays of C127 mouse cells, implying that both L1 and L2 contained neutralising epitopes. This was not tested in cows. Furthermore, only one in five rabbit L2 immune sera tested could neutralise the virus.
However, the prior art does not indicate which element of the papillomavirus L2 protein is the immunogenic element responsible for effective prophylactic therapy, though the work of Christensen et al. and Lin et al. would incline the skilled worker to expect the immunogenic epitope to lie within the carboxy-terminal portion of the peptide. Vaccines produced to date are generally made up of mixtures of various fusion proteins (if produced via recombinant DNA technology) or are of crude extracts of papillomavirus elements or are made up of live virus strains which may display an immunogenic activity in an animal species but which activity may or may not be readily reproducible. Such extracts used as vaccines have not generally been found to work well when applied to other species and do not appear to be particularly efficient.
It is an object of the present invention to provide a more effective prophylactic vaccine against papillomavirus infection in mammals.
It is a further object of the invention to provide a more efficient immunogenically active component for use in a prophylactic treatment of papillomavirus infection.
These and other objects will become apparent from the following description and examples.